This is a recently produced model so raw support was only added in LR 5.7 / ACR 8.7, updates to LR 4 ceased about two years ago when LR 5 was issued.
Options a.) Upgrade to LR 5.
b.) Utilize the latest Adobe DNG Converter 8.8 to convert the nef files to dng format then you will be able to import the dng files into LR 4.
I would recommend a hybrid of those two things: Convert to DNG using the DNGC 8.8, UNTIL LR 6 is available then upgrade to that. It would be disappointing to upgrade to LR 5 then have LR 6 released in a few weeks and have to pay, again.